1. Field of the Invention
The present invention relates to information recording media which has error detecting codes, as pre-format information, for detecting erroneous address numbers. More specifically, the invention relates to information recording media in which it is possible to reduce the cross talk of the reproduced signals of error detecting codes between adjacent tracks in order to securely or reliably detect the errors of the address numbers and read the address information on the tracks.
2. Description of Related Art
The multimedia era having come, optical disks are known as information recording media which can take or cover a great quantity of data such as voice and dynamic images. An optical disk has concentric or spiral tracks which are numbered generally in radially outward (or inward) order. As shown in FIG. 3, each of the tracks is divided into sectors, in each of which information can be recorded and reproduced.
Each of the sectors has pre-format information formed as pre-pits at its front. As shown in FIG. 3, the pre-format information consists mainly of a sector mark, a VFO, an address mark, address data and a CRC (cyclic redundancy check) code. By reading the pre-pits, it is possible to obtain the address information. On the basis of the obtained address information, information is recorded in, and/or read from, the data region of the sector. The sector mark is a data pattern indicating the front of the sector. The VFO (variable frequency oscillator) is a code pattern for timing control in reading the address data positioned just at the back of it. The address mark is a code pattern indicating the starting position or point of the address data. Recorded as the address data are data representing the track number of the associated track and the sector number. The CRC code is an error detecting code for instantaneously detecting whether the address data read out just before it is correct. The CRC code is generated on the basis of the track number and the sector number.
The information recording media proposed for larger capacity in recent years include an optical recording medium having a track pitch narrowed for higher recording density in the directions across the tracks of the medium. The proposed media also include a land-groove (land and groove) type optical recording medium, of which both the lands and the grooves are used as tracks for higher recording density. The pre-pits in the sectors of an optical recording disk are adjacent to each other in the radial direction. Therefore, if the track pitch of the disk is narrowed, or if both the lands and the grooves of the disk are used as tracks, the pre-pits in each track of the disk are close to those in the adjacent tracks. Consequently, when information is read from the pre-pits in one of the tracks, signals may leak from the pre-pits in the adjacent tracks, that is to say, cross talk may occur.
In particular, because the CRC code of the pre-format information is generated on the basis of the track and sector numbers, the data trains of the CRC codes in the xe2x80x9cnxe2x80x9dth track from which information is being read differs entirely from those of the CRC codes in the adjacent xe2x80x9cn+1xe2x80x9dth and xe2x80x9cnxe2x88x921xe2x80x9dth tracks. This makes cross talk liable to affect the CRC codes. If it is impossible under the influence of cross talk to correctly read out the CRC codes for detection of errors, it is impossible to correctly detect whether the address data read out before each CRC code is accurate. In other words, even if the address data is correctly read out, it may be judged to be erroneous. Accordingly, the cross talk from the adjacent tracks is a very serious problem in address data error detection.
In the land-groove type optical recording medium, sector marks and/or ID data which include address information are recorded in both the lands and grooves. For example, when information is read from one of the lands (or grooves), cross talk occurs from the adjacent grooves or groove (or lands or land), making it difficult to correctly read the address information from the lands.
In view of the above problems, Japanese Patent Application Laid-Open No. 8-339540 discloses an optical recording medium for recording in lands and grooves. This recording medium has sectors each including a sector ID region. This ID region consists of a sector mark indicating the front of the sector, an ID data zone and a space without a pit. The space of each of the sector ID regions formed in a groove is positioned adjacent to the ID data zone of one of the sector ID regions formed in a land. Likewise, the space of each of the sector ID regions in a land adjoins the ID data zone of one of the sector ID regions in a groove. Specifically, each sector ID region in each groove consists of a sector mark, a space and an ID data zone in that order, while each sector ID region in each land consists of a sector mark, an ID data zone and a space in that order. Each of the ID data zones is a data train consisting of a VFO, an address mark, address data and a CRC code.
The space of each sector ID region is equivalent in area to the ID data zone, which consists of a VFO, an address mark, address data and a CRC code, of each sector ID region. The area of the spaces of the sector ID regions restricts the recording capacity of the optical recording medium. The capacity restriction does not match the need for recording densification or higher recording density.
The present invention has been made for solution of the problems with, and the disadvantages of, the prior art. A first object of the invention is to provide an information recording medium having novel error detecting codes as pre-format information which can be less affected by cross talk from the adjacent tracks.
A second object of the invention is to provide an information recording medium which can be less affected by cross talk from the adjacent tracks, and which can realize larger capacity.
A third object of the invention is to provide a novel error detecting method which can detect the error of address information reliably with little influence of cross talk from the adjacent tracks.
According to a first aspect of the invention, there is provided an information recording medium having a plurality of tracks each sectioned into sectors, the medium being characterized in:
that each of the sectors has a mark representing address data which represents the address of the associated sector and a mark representing an error detecting code for detection of the error of the address data; and
that the error detecting codes of the tracks are so formed that the distance between the detecting codes of any adjacent tracks is always 1.
The error detecting codes for detection of the errors of the address data of this information recording medium are so formed that the distance between the codes of adjacent tracks is always 1. In other words, the detecting codes are constructed in such a manner that, when the codes of adjacent tracks are compared, there is only one reverse bit. Consequently, when the detecting code of one of adjacent tracks is read out, there is only one place where signal leakage (cross talk) may occur from the other track. This minimizes the influence of cross talk. Therefore, even if the recording medium has a narrow track pitch, it is possible to reliably read out the detecting codes, making it possible to reliably detect the errors of the address data.
In this specification, the term xe2x80x9cmark/sxe2x80x9d is/are the concept of any marks formed by changes in physical or chemical shape, material or structure. The marks may be pits formed in any shape in a substrate, magnetic marks formed in accordance with the directions of magnetization on a magnetic film, marks formed on the basis of a change of phase between the crystalline and amorphous substances on a phase change film, or marks formed on the basis of a change of shape or material with heat, light and/or the like on an organic pigment film.
In this invention, generation of such error detecting codes that the distance between the codes of adjacent tracks is always 1 may involve generating check bits for parity checks on the basis of the sector numbers and the Gray coded track numbers, and forming or constructing the detecting codes out of the check bits. A method of generation as an example will be described below in detail, but the invention is not limited to it.
First, the bits of the track number of a track are expressed as T1, T2, . . . , Tnxe2x88x921, and Tn, and the bits of the data train representing the sector number of a sector of this track are expressed as S1, S2, . . . , Smxe2x88x921 and Sm (m less than n). It is assumed that the track number represented as bits of data has been Gray coded by a method described later. If the bits of the error detecting code for this sector are expressed as E1, E2, . . . , Emxe2x88x921 and Em in ascending order, the bits are expressed as shown in FIG. 7. For simplification, the number of bits of the detecting code is equal to that of the sector number. The number of bits of the code might, however, be arbitrary. In FIG. 7, Prepresents a check bit for a parity check. An even parity check involves adding a check bit xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d to the data train in such a manner that the total number of 1""s in a data train is always an even number. An odd parity check involves adding a check bit xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d to the data train in such a manner that the total number of 1""s in a data train is always odd. When the thus obtained trains of error detecting codes of adjacent tracks are compared, the distance between the codes is 1. In order to detect the error of address data consisting of a track number and a sector number, it is possible to judge or decide whether the total number of 1""s in the data train consisting of the address data and the associated error detecting code is even or odd. Specifically, for an even parity check, when the data train consisting of address data and the associated error detecting code is read out, it is found that there is no error in the address data if the total number of 1""s in this data train is even, while there is an error in the address data if the total number is odd.
The Gray coding of a track number will be described below. Gray coding is such conversion of serial data trains that one bit differs between the xe2x80x9cnxe2x88x921xe2x80x9dth and xe2x80x9cnxe2x80x9dth trains and between the xe2x80x9cnxe2x80x9dth and xe2x80x9cn+1xe2x80x9dth trains, that is to say, the distance between the codes is 1, and that the xe2x80x9cnxe2x88x921xe2x80x9dth and xe2x80x9cn+1xe2x80x9dth converted trains differ from each other. A track number may be converted into a Gray code as follows.
If a track number is expressed as an n-bit binary number, the bits of which are expressed as tn, tnxe2x88x921, tnxe2x88x922, . . . , t2 and t1, then the bits gn, gnxe2x88x921, gnxe2x88x922, . . . , g2 and g1, of the Gray coded number are expressed by the following expressions:
gm=tm+1{circumflex over ( )}tm
(where m=1, 2, . . . , nxe2x88x921, and {circumflex over ( )} represents exclusive OR) gn=tn.
That is to say, the exclusive OR operation of the first bit t1, and the second bit t2 of the n bits is performed, and the resultant value is made the first bit g1 of the Gray coded number. Next, the exclusive OR operation of the second bit t2 and the third bit t3 of the n bits is performed, and the resultant value is made the second bit g2 of the Gray coded number. Likewise, the exclusive OR operation of the xe2x80x9cnxe2x88x921xe2x80x9dth bit tnxe2x88x921 and the xe2x80x9cnxe2x80x9dth bit tn of the n bits is performed, and the resultant value is made the xe2x80x9cnxe2x88x921xe2x80x9dth bit gnxe2x88x921 of the Gray coded number. One bit equal to the highest bit tn of the number before Gray coding is added to the highest bit gn of the Gray coded number. In this way, all track numbers are converted in order into Gray codes. The distance between the codes of adjacent tracks is 1. One bit differs between the Gray coded track numbers of adjacent tracks. This makes it possible to reduce the influence of cross talk on not only the error detecting codes but also the track numbers, enabling the track numbers to be read out reliably.
According to a second aspect of the invention, there is provided an information recording medium having a plurality of tracks each sectioned into sectors, the medium being characterized in:
that each of the sectors has marks representing pre-format signals;
that the pre-format signals include a sector mark representing the front of the associated sector, a VFO for timing control in reading data, an address mark representing the position from which address data starts to be read out, address data representing the address of the sector, and a CRC code for detection of the error of the address data; and
that one of any adjacent tracks has blank data just before each of the CRC codes thereof, while the other track has blank data just behind each of the CRC codes thereof, so that the CRC codes of the adjacent tracks do not adjoin.
As shown in FIG. 12, this information recording medium is provided with blank data just-behind the CRC code of the track 0 (or 1) and blank data just before the CRC code of the track 1 (or 2) adjacent to the track 0 so that the zones of the codes of each track are offset from those of the other track. This makes it possible to reduce the occurrence of cross talk from the pre-pits in adjacent tracks without substantially reducing the recording capacity of the recording medium. This recording medium requires blank data only before and behind the CRC codes, in contrast to the format disclosed in Japanese Patent Application Laid-Open No. 8-339540, for the following reason.
As stated in the Related Art section, the CRC codes of the pre-pits formed in advance in an information recording medium are generated on the basis of the track numbers and the sector numbers. Consequently, the CRC codes of each track are data trains different entirely from those of the adjacent tracks, and are subject to the influence of cross talk. In contrast, the other data of the pre-pits, which may include sector marks, VFOs and address marks, are the same data trains for all the sectors, and are therefore little or less subject to the influence of cross talk. The sector numbers of the address data of the pre-pits are the same for the sectors adjacent in the directions across the tracks (the sectors at the circumferentially same position of a recording medium in disk form). Therefore, the sector numbers are little or less subject to the influence of cross talk likewise. The inventors have directed their attention to this point, and provided blank data having the same length as each of the CRC codes before or behind each of these codes, which are subject to the influence of cross talk, in order for the blank data to offset the CRC codes so that the codes of each track do not adjoin those of the adjacent tracks. In the tracks of odd (or even) track numbers, blank data may be positioned just behind each of the CRC codes. In the tracks of even (or odd) track numbers, blank data may be positioned just before each of the CRC codes. This interposes each CRC code of each track between the blank data (of the adjacent sectors) of the adjacent tracks. Consequently, when the CRC codes of each track are read out, no signal leakage (cross talk) occurs from the CRC codes of the adjacent tracks. It is therefore possible to reliably read out the CRC codes, making it possible to reliably detect the errors of the address data. Because the blank data are equal in length to the CRC codes, the recording capacity is not reduced substantially.
In this invention, the blank data may be zones each formed with no mark or a continuous mark. In this case, even if signals leak from pre-pits in adjacent tracks, the values of the leaking signals do not change, but are always constant. Therefore, the signal leakage does not affect the reading of reproduced signals from the CRC codes of a desired track.
It is preferable that the track numbers in the information recording medium according to the second aspect of the invention be converted into Gray codes. The track numbers can be converted into Gray codes by the foregoing Gray coding method. The conversion results in (or leads to) one place in the track number of each track where the bit differs from that of the track number of an adjacent track, that is to say, two places in the track number of each track where each of the bits differs from that of the track number of one of the adjacent tracks. This reduces the number of places where cross talk may occur. It is therefore possible to reliably read out the track numbers.
According to a third aspect of the invention, there is provided an error detecting method for detecting the error of address information including a track number which represents the position of a track and a sector number which represents the position of a sector, the method being comprising the steps of:
converting the track number into a Gray code;
dividing the Gray coded track number and the sector number to obtain a plurality of data groups;
generating such parity check bits each from one of the data groups that the distance between the codes of adjacent tracks is 1; and
detecting the error of the address information by using the check bits.
This error detecting method may include expressing the Gray coded track number as a train of 16 bits T1T2, . . . , T15T16 and the sector number as a train of 4 bits S1S2S3S4, and dividing the bits of these trains into data groups A1-A4 as shown in FIG. 8. The data groups might be replaced by data groups B1-B4, data groups C1-C4 or data groups D1-D4 as shown in FIG. 9. Check bits for even or odd parity checks are made up from the data groups A1-A4. Error detecting codes are generated from the check bits. The distance between the error detecting codes of adjacent tracks is always 1. Accordingly, when the error detecting code of a desired track is read out, the influence of cross talk from the adjacent tracks is reduced.
To this error detecting method as well, the foregoing Gray coding method can be applied as a method for converting a track number into a Gray code.